The present invention generally relates to ultrasound imaging of anatomical structures. In particular, the invention relates to a method and system for improving the display of ultrasound imaging of anatomical structures.
For a number of years, ultrasound imaging has been used to non-invasively monitor and image anatomical structures within the human body. To produce the image, an ultrasonic transducer transmits an ultrasonic wave of energy into a patient's body. The properties of ultrasonic echoes returning from various structures and elements within the patient's body are then used to produce frames of data referred to as image frames. As the image frames are acquired, they may be displayed on a monitor, output to a printer, and/or stored in a memory for playback at a later time.
The human body is not an immobile object. Patient's breathe, blood flows, and tissues move. Because tissues within the patient move during the course of an ultrasound procedure, corresponding tissue structures in successive image frames may appear in different portions of the image frames. Combining data from successive image frames where corresponding tissue structures are misaligned blurs the boundaries between tissue structures and reduces the overall quality of the combined image.
For example, ultrasound is sometimes used to track the flow of fluids in a patient's body. To highlight the flow of fluids in the patient's body, the patient is sometimes injected with a contrast agent, the progression of which is tracked using the ultrasound system. Shortly after the contrast agent is injected, the ultrasound system starts acquiring images, oftentimes set up to scan in special imaging modes designed to preferentially image contrast agents. As the contrast agent flows through the patient's body, successive image frames are continuously acquired.
To display the entire path traversed by a contrast agent as it progresses through the body, a peak display image may be produced that shows the maximum concentration of contrast agent at various points in the body during acquisition of the image frames. To produce the peak display image, a first image frame is acquired. A second image frame is acquired and each pixel of the second image frame is compared with each pixel of the first image frame. The highest value for each pixel amongst the second image frame and the first image frame is used to create a peak display image. Next, a third image frame is obtained and each pixel in the third image frame is compared with corresponding pixels of the peak display image. Pixel intensity values in the third image frame that exceed corresponding pixel values in the peak display image replace the corresponding pixel value in the peak display image to produce an updated peak display image. The process is repeated for each subsequently acquired image frame such that each time a pixel value in a recently acquired image frame exceeds a corresponding pixel value in the peak display image, the pixel value in the recently acquired image frame replaces the corresponding pixel value in the peak display image. Consequently, a running tally is kept of the entire path traversed by contrast agent from the acquisition of the first image frame all the way to the currently acquired image frame.
However, as the successive image frames are acquired, tissues within the patient are moving and corresponding tissue structures in the successive image frames are represented by different pixels. Because the corresponding tissue structures are represented by different pixels in successive image frames, comparing and combining images with misaligned tissue structures pixel to pixel reduces the quality of the combined image. The quality of the image is reduced because misaligned tissue structures in images being compared can result in pixels for body anatomy such as a vein being compared with pixels for a strong reflector such as a tendon resulting in peak values for the tendon possibly replacing values for the vein in the peak display image. Consequently, such misalignment of corresponding tissue structures in successive image frames can blur the boundaries between tissue structures, such as the vein and the tendon, in the peak display image. As a result, prior art systems are susceptible to motion artifacts and blurring because a significant amount of tissue motion can occur during the course of an entire ultrasound procedure.
While an example using contrast agent imaging and a peak display image has been presented, misalignment of corresponding tissue structures is a problem for other ultrasound imaging modes as well. For example, misalignment of corresponding tissue structures effects color flow imaging and B flow imaging.
One solution for reducing the effects of tissue motion on a combined image includes spatial correlation measures. With spatial correlation measures, each image frame is processed and compared with other prior and subsequent image frames to correlate pixels in an image frame with pixels representing the same tissue in prior and subsequent image frames. Due to the sheer number of pixels, comparisons, and correlations, re-aligning corresponding tissue structures using spatial correlation measures requires substantial time and software processing. Delays in image processing due to processing time reduce patient throughput and waste valuable technician time.
Consequently, a need exists for a system that allows for the creation of an accurate peak display image with a reduction in the effects of tissue motion on image quality and accuracy. Additionally, a need exists for a system that reduces the effects of tissue motion without using spatial correlation measures that require substantial time and software processing.